PROJECT SUMMARY/ ABSTRACT Therapeutic antibodies have achieved great success in a variety of diseases such as autoimmune disorders and cancers; however, their therapeutic potential has not been fully realized yet. Many FDA-approved antibodies now face high therapeutic hurdles, such as inadequate efficacy in monotherapy and high rates of resistance. Some hurdles can be overcome by engineering new antibody entities with either improved target selectivity or functionality. Many others remain unresolved, as they are not just about the antibody itself, rather essentially as a result of antibody discordant interactions with the host system. For instance, CD20-targeted antibodies often confront resistance that is due to overwhelming antibody exposure to the immune system leading to exhausted effector function and then loss of drug sensitivity. To resolve those issues, we plan to develop a system platform that collectively consolidates the fundamental properties of the antibody and the host system, and integrate their spatial/temporal coordination. If it is established, this platform will alleviate or even sidestep these therapeutic hurdles and facilitate efforts to optimize the current antibody-based therapies. We will develop this system platform on multiple scales from cells to the whole body, by collectively evaluating all steps of antibody actions from dosing to final responses. Specifically, we will collaborate with experts in the fields of radiology and molecular imaging to develop novel labeling approaches to track antibody entities at multiple levels (i.e., blood, tissue, interstitial fluid, and cell) and assess antibody system persistence and distribution to the site(s)-of-action (pharmacokinetics) (Project 1). We will apply a series of combined experimental and computational approaches to assess the temporal and spatial antibody- antigen interactions in vivo, and the subsequent cellular and subcellular events (Project 2). Advanced cell- labeling methods will be applied to monitor lymphocyte migration, infiltration, functional orientation, and dynamics of effector function (e.g., Fc?R) and the complement system (e.g., C3 and C4) in the tumor microenvironment. Patient-derived blood and solid tumors will be used to prepare lymphocytes, on which dynamics of effector function will be assessed. This will better mimic the tumor environment and increase our ability to predict patient responses. Antibody therapy will be further tailored to coordinate the status of immune system and the dynamics of effector function for maximal effect (Project 3). All these quantitative studies will support this system platform to facilitate the proper selection of an antibody, determine the precise dose and dosing interval to attain the desired target exposure and target engagement. The time course of target binding will coordinate physiology and dynamics of the immune system to achieve optimal treatment.